1. Field of the Invention
The present invention relates to a slim cathode ray tube, and, more particularly, to a panel for color cathode ray tubes wherein the thickness of the center of the panel, and the thicknesses of a seal edge are appropriately set, and the outer skirt angle of the panel is appropriately set, thereby minimizing the concentration of stress caused due to the increase of a deflection angle, providing sufficient rigidity, improving the explosion-resistance characteristic and moldability of the panel, and effectively preventing slippage of a reinforcing band.
2. Description of the Related Art
Generally, a cathode ray tube is an apparatus that converts an electric signal into an electron beam and scans the electron beam on a fluorescent screen to display picture on a panel.
FIG. 1 is a side view, partially cut away, illustrating a conventional cathode ray tube, and FIG. 2 is a sectional view illustrating a panel constituting the conventional cathode ray tube.
As shown in FIGS. 1 and 2, the conventional cathode ray tube comprises a panel 1 and a funnel 2, which are joined with each other to constitute a tube part 10.
Inside the panel 1 is disposed a shadow mask 3, which is supported by a frame 4 such that the shadow mask 3 is approximately parallel with the panel 1. The frame 4 is fixed to the panel 1 via a spring 5. Inside the funnel 2 is disposed an inner shield 6 for shielding an external geomagnetic field to prevent the path of an electron beam from being curved by the external geomagnetic field.
In the rear part of the funnel 2 is fitted an electron gun 7 for generating an electron beam. At the outside of a neck part of the funnel 2 is mounted a deflection yoke 8 for deflecting an electron beam approximately 110 degrees or less.
In the conventional cathode ray tube with the above-stated construction, an electron beam emitted from the electron gun 7 is deflected above and below and right and left by the deflection yoke 8, and is then transmitted to the panel 1. Specifically, the deflected electron beam passes through-holes of the shadow mask 3, and is then transmitted to a fluorescent screen 9 coated on the inner surface of the panel 1. At this time, the fluorescent screen 9 is illuminated by the energy of the electron beam. Consequently, a picture is reproduced such that users can see the picture reproduced through the panel 1.
Meanwhile, the panel 1 and the funnel 2 are joined to each other at a seal edge 1x, 1y, and 1d of the panel 1 by a frit sealing process, the electron gun 7 is fitted into the rear part of the funnel 2 by a subsequent encapsulation process, and a vacuum is formed in the tube part 10 by an extraction process. In this way, the cathode ray tube is manufactured.
When the tube part 10 is in the vacuum state, considerable tensile and compression stresses are applied to the panel 2 and the funnel 2.
Especially when the overall length of the tube part 10 is decreased, the inner volume of the tub part 10 is correspondingly decreased. As a result, stress applied to the tube part 10 is increased. Recently, the neck part of the funnel 2 has been formed in the shape of a rectangle to reduce current necessary for the deflection of an electron beam, and thus, to reduce the power consumption of the deflection yoke 8. In this case, however, stress applied to the tube part 10 is further increased.
Referring to FIG. 2, CFT indicates the thickness of the center of the panel 1, and SET indicates the thickness of the seal edge of the panel 1, at which the panel 1 and the funnel 2 are joined with each other. Specifically, SET(Tx) indicates the thickness of the seal edge of the panel 1 at the long side part, SET(Ty) indicates the thickness of the seal edge of the panel 1 at the short side part, and SET(Td) indicates the thickness of the seal edge of the panel 1 at the diagonal part.
When CFT of the panel 1 is decreased, stress of the tube pat 10 is concentrated on the panel 1. When SET (Tx, Ty, Td) of the panel 1 is decreased, on the other hand, stress is concentrated on the seal edge of the panel 1, and therefore, a possibility for the tube part 10 to be damaged is increased.
Consequently, the CFT and SET setting is very important to appropriately distribute the stress of the panel 1. Specifically, when CFT and SET are large, the stress is prevented from being concentrated on a specific portion of the panel 1, as shown in FIG. 3. However, the total volume of the panel 1 is increased, and therefore, manufacturing costs of the panel 1 are also increased.
In conclusion, setting CFT and SET of panel 1 is a process of finding the optimum point at the relationship between the stress and the costs.
In the conventional cathode ray tube having the 110-degree deflection structure as described above, the length of the funnel 2 is greater than that of the panel 1, and the neck part of the funnel 2 is formed in the shape of a smooth curve. Consequently, stress is not concentrated on the funnel 2, and therefore, it is not necessary for the stress to be distributed.
For this reason, the panel 1 is designed such that the ratios of CFT to SET(Tx, Ty, Td) of the panel 1 are the same over all regions as shown in FIG. 4. When the ratios of CFT to SET(Tx, Ty, Td) of the panel 1 were changed, there was no difference in stress, and the reduction of costs was slight. Specifically, the ratios of CFT to SET were slightly different depending upon the size and deflection angle of the tube part 10.
However, the slim cathode ray tube, which has been developed recently, has a deflection structure with a deflection angle of 110 degrees or more. Also, the overall length of the slim cathode ray tube is decreased, and therefore, the inner volume of the slim cathode ray rube is reduced. As a result, stress is further applied to the panel and the funnel. Consequently, it is required that the ratios of CFT to SET of the panel 1 be appropriately set to effectively prevent excessive stress from being applied to the panel and funnel.
Meanwhile, when the tube part 10 is in a vacuum state, considerable tensile and compression stresses are applied to the panel 1 and the funnel 2. Referring to FIGS. 2 and 5, when the tube part 10 is in the vacuum state, the stress of the panel 1 against external impact is transmitted to the funnel 2 via the seal edge 1x, 1y, and 1d at the end of a side wall is of the panel 1. As a result, the stress of the panel 1 is somewhat reduced.
Consequently, the thickness SET and the shape of the side wall is of the panel 1, i.e., the seal edge 1x, 1y, 1d of the panel 1 both have considerable influence on the reliability of the cathode ray tube.
Especially, the explosion-resistance characteristic to external impact and a sparking phenomenon, which is generated when the tube part 10 passes through a furnace such that the panel 1 and the funnel 2 are joined with each other by frit welding at the time of manufacturing the cathode ray tube, are deeply connected with the thickness and the shape of the seal edge of the panel. Furthermore, when the outer skirt angle S of the side wall 1s is increased, the productivity in the manufacture of the tube 10 is decreased.
In the conventional panel 1, the outer skirt angle S is approximately 3 to 4 degrees. The outer skirt angle S is the greatest at the long side part 1x. The outer skirt angle S is the least at the short side part 1y. The outer skirt angle S at the diagonal part 1d is less than the outer skirt angle S at the long side part 1x and greater than the outer skirt angle S at the short side part 1y. 
In the panel 1 of the cathode ray tube as described above, the outer skirt angle S of the panel 1 is 3 degrees or more, and the outer skirt angle S is set such that the outer skirt angle S is the greatest at the long side part 1x, the outer skirt angle S is the least at the short side part 1y, and the outer skirt angle S at the diagonal part 1d is less than the outer skirt angle S at the long side part 1x and greater than the outer skirt angle S at the short side part 1y. As a result, the thickness SET of the long side part 1x is less than that of the short side part 1y, and therefore, the explosion-resistance characteristic is lowered.
Furthermore, a reinforcing band 11 is wound around the side wall 1s, as shown in FIG. 1, to distribute high stress applied to the panel 1. When the outer skirt angle S of the panel 1 is large as described above, however, the reinforcing band 11 can easily slip. Consequently, it is difficult to perform the reinforcing band winding process, and it is difficult to effectively distribute stress applied to the tube part 10 when the reinforcing band 11 slips.